Interpretive Summary: Cattle are known carriers of Escherichia coli O157:H7 and other illness-causing pathogens, and most cases of human sickness associated with O157:H7 in the United States are either directly related to consumption of contaminated beef or are traced to contamination of other foods associated with cattle. No E. coli O157:H7 was found in monthly samples of the feces of Florida heifers and steers for the duration (over three years) of this project. In this study, the presence of other illness-causing pathogens, including Salmonella and Campylobacter, was not associated with different cattle breeds. These results imply that choice of cattle breed or crossbreeding would not effectively control fecal shedding of Salmonella or Campylobacter in cattle. It also suggests that young cattle produced in different years from a single herd and maintained as a group can apparently be O157:H7 free over long periods of time, even through high risk times such as the feedlot phase. Results suggest that beef cow-calf operations may not be the best focus for programs to minimize O157:H7 in the beef production chain.

Technical Abstract:
The objective in this study was to assess breed effects in fecal prevalence of Escherichia coli O157:H7 in heifers on a development program in Florida and in their half-sibling steers in stocker and feedlot phases in Oklahoma. A secondary objective was to characterize fecal shedding of Campylobacter, enterococci, generic E. coli, and Salmonella in subsets of the same animals. After weaning, heifers (n = 485; purebreds and F1 crosses of Angus, Brahman, and Romosinuano) were preconditioned and placed in a local development program. Steers (n = 481) were transported to Oklahoma where they grazed wheat for six months, and then placed in feedlot pens. Fecal samples were obtained for 12 months on all animals. Of the 10,982 samples, none tested positive for E. coli O157:H7. Fecal prevalences of Campylobacter, enterococci, generic E. coli, and Salmonella in heifers were 1.7, 88.5, 84.1, and 0.04%, respectively. Corresponding steer percentages were 27.2, 83.4, 90.8, and 0.6%. Campylobacter isolates were mostly C. jejuni and tetracycline-resistant. Eight Salmonella isolates were S. Typhimurium and quad- or penta-resistant, most often to ampicillin, chloramphenicol, sulfamexathole, and tetracycline. Heifers on summer pastures had greater odds (odds ratio [OR] 3.0, confidence interval [CI] 1.5, 6.0) of positive detection of generic E. coli and enterococci (OR 1.9, CI 1.1, 3.3) than during winter feeding. Steers in the feedlot had greater odds of positive detection of Campylobacter (OR 8.5, CI 3.7, 19.5) but lower for enterococcus (OR 0.1, CI 0.04, 0.25) than when grazing winter wheat. No breed effect was detected for these enterobacteriaceae.